Wireless communication networks are well known. Some networks are completely proprietary, while others are subject to one or more standards to allow various vendors to manufacture equipment for a common system. One such standards-based network is the Universal Mobile Telecommunications System (UMTS). UMTS is standardized by the Third Generation Partnership Project (3GPP), a collaboration between groups of telecommunications associations to make a globally applicable third generation (3G) mobile phone system specification within the scope of the International Mobile Telecommunications-2000 project of the International Telecommunication Union (ITU). Efforts are currently underway to develop an evolved UMTS standard, which is typically referred to as UMTS Long Term Evolution (LTE) or Evolved UMTS Terrestrial Radio Access (E-UTRA).
According to Release 8 of the E-UTRA standard, downlink communications from a base station (referred to as an “enhanced Node-B” or simply “eNB”) to a wireless communication device (referred to as “user equipment” or “UE”) utilize orthogonal frequency division multiplexing (OFDM). In OFDM, orthogonal subcarriers are modulated with a data stream. The subcarriers may be contiguous or discontiguous and the downlink data modulation may be performed using quadrature phase shift-keying (QPSK), 16-ary quadrature amplitude modulation (16 QAM), or 64 QAM.
In contrast to the downlink, uplink communications from the UE to the eNB utilize single-carrier frequency division multiple access (SC-FDMA) according to the E-UTRA standard. In SC-FDMA, block transmission of QAM data symbols is performed by first discrete Fourier transform (DFT)-spreading (or preceding) followed by subcarrier mapping to a conventional OFDM modulator. The use of DFT preceding allows a moderate cubic metric/peak-to-average power ratio (PAPR) leading to reduced cost, size and power consumption of the UE power amplifier. In accordance with SC-FDMA, each subcarrier used for uplink transmission includes information for all the transmitted modulated signals, with the input data stream being spread over them. The data transmission in the uplink is controlled by the eNB, involving transmission of scheduling requests (and scheduling information) sent via downlink control channels. Scheduling grants for uplink transmissions are provided by the eNB on the downlink and include, among other things, a resource allocation (e.g., a resource block size per one millisecond (ms) interval) and an identification of the modulation to be used for the uplink transmissions. With the addition of higher-order modulation and adaptive modulation and coding (AMC), large spectral efficiency is possible by scheduling users with favorable channel conditions.
E-UTRA systems also facilitate the use of multiple input and multiple output (MIMO) antenna systems on the downlink to increase capacity. As is known, MIMO antenna systems are employed at the eNB through use of multiple transmit antennas and at the UE through use of multiple receive antennas. A UE may rely on a pilot or reference symbol (RS) sent from the eNB for channel estimation, subsequent data demodulation, and link quality measurement for reporting. The link quality measurements for feedback may include such spatial parameters as rank indicator, or the number of data streams sent on the same resources; preceding matrix index (PMI); and coding parameters, such as a modulation and coding scheme (MCS) or a channel quality indicator (CQI). For example, if a UE determines that the link can support a rank greater than one, it may report multiple CQI values (e.g., two CQI values when rank=2). Further, the link quality measurements may be reported on a periodic or aperiodic basis, as instructed by an eNB, in one of the supported feedback modes. The reports may include wideband or subband frequency selective information of the parameters. The eNB may use the rank information, the CQI, and other parameters, such as uplink quality information, to serve the UE on the uplink and downlink channels.
To facilitate demodulation of uplink transmissions and measurement of uplink channel conditions, the UE typically transmits reference symbols in each uplink subframe. The reference symbols are multiplexed together with the control information (e.g., CQI and rank information) and any data to be sent by the UE on the uplink data channel (referred to as the physical uplink shared channel (PUSCH)). According to the E-UTRA standard, the UE may also transmit hybrid automatic repeat request acknowledgments (HARQ-ACK) acknowledging receipt of prior data transmission from the eNB to the UE (also referred to as downlink data transmission). In a Frequency Division Duplex (FDD) implementation, the UE transmits the HARQ-ACK in a subframe for a prior data transmission from the eNB to the UE sent four milliseconds earlier. For a Time Division Duplex (TDD) implementation, the timing relationship between the downlink data transmission and the corresponding uplink HARQ-ACK transmission may be different. Such HARQ-ACKs, when transmitted, form part of the control information transmitted in an uplink subframe.
In the absence of uplink data to be sent, a UE may transmit uplink control information on an uplink control channel, such as a physical uplink control channel (PUCCH). Control signaling on the PUCCH is transmitted in a reserved frequency region near the edges of a carrier band. Multiple PUCCHs (e.g., for HARQ-ACK, CQI, scheduling requests, etc.) are assigned per resource for different UEs using orthogonal coding. However, in some cases according to the E-UTRA standard, uplink control information must be transmitted over an uplink data channel instead of an uplink control channel either together with data or in the absence of data.
The procedure for modulating and coding of the uplink control information when accompanying the transmission of data is based on the MCS employed for the data as instructed by the eNB in a scheduling grant message. In other words, the MCS for the control information is based on the MCS for the particular data accompanying the control information. The linkage between the data MCS and the control information MCS is given by Contribution R1-081852 to the 3GPP Radio Access Network (RAN) Working Group 1 (3GPP RANI) as the following equation (Equation 1):
            M      ctrl        =          ⌈                        N          ·                      CR                          M              Mod                                                10                                    -                              offset                ⁢                _                ⁢                dB                                      10                              ⌉        ,where Mctrl is the number of control symbols per transmit time interval (TTI) (e.g., a 1 ms subframe); offset_dB is the performance difference between a given control channel and a PUSCH in decibels (dB); N is the number of control signaling bits (for a given control signaling type); CR is the inverse coding rate of a given PUSCH MCS (e.g., 3/1); MMod is the number of (uncoded) bits per symbol of PUSCH MCS (e.g., 2, 4 or 6) based on the uplink modulation (e.g., QPSK, 16 QAM, 64 QAM); and the function (┌•┐) rounds the control channel size to the nearest supported integer value towards positive infinity. The supported integers are based on the coding/repetition/puncturing assumptions made for given control signaling on the PUSCH. While Equation 1 provides the underlying principles for determining the control MCS based on the data MCS, the formula has been modified (although not substantially) and simplified in the final version adopted in the E-UTRA standard.
FIG. 1 illustrates a logical block diagram for channel coding and multiplexing functions performed by a processor 100 in an E-UTRA UE to generate a subframe 113 for transmission of control information and data over a PUSCH in accordance with the linkage specified in Equation 1 above. The processor 100 includes, among other things, channel coding blocks 101, 103, 105, 107 for the uplink data and for each respective portion of control information (e.g., CQI, rank, and ACK/NACK). The processor 100 also includes coding blocks for uplink reference symbols and for any other included control information; however, the coding and multiplexing for the reference symbols and other types of control information have been omitted from FIG. 1 for simplicity and clarity.
In accordance with the E-UTRA standard, to request uplink data from a UE, the eNB transmits a scheduling message (e.g., a scheduling grant message) via downlink control information (DCI) on a downlink control channel (e.g., a physical downlink control channel (PDCCH)) providing parameters for the uplink transmission. The parameters provided by the eNB for use in generating the uplink subframe include data modulation format, resource allocation (e.g., resource blocks and position within overall system bandwidth), power control information, and other control information. In the event that the eNB requires aperiodic or as-requested CQI reporting by the UE, the other control information would include a one bit CQI reporting request.
Based on the parameters supplied in the scheduling grant message, the UE creates a data-carrying SC-FDMA subframe according to the linkage provided in Equation 1. According to the E-UTRA standard, each subcarrier of an assigned uplink resource block is divided in time elements referred to as “resource elements.” A typical resource block has a bandwidth of 180 kHz and includes 12 subcarriers per 1 ms subframe. The resource elements contain encoded SC-FDMA symbols spread across the subcarriers, such that a typical subframe includes 14 SC-FDMA symbols. Two of the 14 symbols are reference or pilot symbols used for demodulation of the uplink channel by the eNB and/or determining uplink channel quality. Additionally, the UE may also transmit a sounding reference signal (SRS) on one of the 14 symbols which is not associated with uplink data and/or control transmission. The SRS, when transmitted, is primarily used for channel quality determination to enable frequency selective scheduling on the uplink. The remaining 12 symbols (or 11 if SRS is present) per subframe are encoded with the uplink data and control information. The encoding of the control information and the multiplexing of the encoded control information into the subframe is based on the MCS for the data, which was supplied by the eNB in the scheduling grant message, as set forth in Equation 1.
As illustrated in FIG. 1, the uplink data and its associated error correction information are encoded by channel coding block 101 according to the data MCS supplied in the scheduling grant message. The CQI and its associated error correction information are encoded according to Equation 1 by channel coding block 103. Similarly, the rank information, when included, is encoded according to Equation 1 by channel coding block 105. Further, ACK/NACK information, when included, is encoded according to Equation 1 by channel coding block 107. The encoded uplink data and encoded CQI are multiplexed by multiplexing block 109 and provided to the channel multiplexing block 111. The channel multiplexing block 111 then multiplexes the multiplexed encoded data and CQI together with the encoded rank and ACK/NACK information onto the subcarriers of the resource block according to a predetermined multiplexing procedure that is based on the data MCS. The channel multiplexing block 111 produces the uplink data channel subframes 113. An exemplary subframe 113 is illustrated in FIG. 2.
As shown in FIG. 2, the exemplary subframe 113 includes a resource block of twelve subcarriers (sub0 through sub11), each of which is divided into fourteen time segments (t0 through t13). Each time segment on a particular subcarrier is a resource element 301. The subframe 113 is further broken into two equal time slots (Slot 0 and Slot 1). Each resource element 301 includes a portion of the encoded uplink data (denoted “D” in the exemplary subframe 113), a portion of a particular type of encoded control information (denoted “C” for CQI, “RI” for rank information, and “AN” for ACK/NACK information in the exemplary subframe 113), or a portion of a reference symbol (denoted “RS” in the exemplary subframe 113). The set of resource elements 301 spread across all 12 subcarriers during a particular segment of time forms an SC-FDMA symbol.
The channel multiplexing block 111 typically forms the subframe 113 by first inserting the reference symbols as the fourth symbol of each time slot of the subframe. After the reference symbols have been inserted, the rank information, when included, is inserted into resource elements 301 commencing at the lowest frequency subcarrier edge (sub0) of the subframe 113 and continuing across each subcarrier in the second, sixth, ninth, and thirteenth symbols of the subframe 113 until all the encoded rank information has been added to the subframe 113. Thereafter, the CQI information is inserted into unoccupied resource elements 301 commencing at the highest frequency subcarrier edge (sub11) of the subframe 113 and continuing across each subcarrier in every symbol of the subframe 113, except for the fourth and eleventh symbols (which contain the reference symbols) and avoiding the subcarriers occupied by the rank information, until all the encoded CQI information has been added to the subframe 113. Following insertion of the CQI information, the encoded data is added to the subframe 113 into all the remaining, unoccupied resource elements 301. If encoded ACK/NACK information is to be transmitted, such information is thereafter added to the subframe 113 in the resource elements 301 forming some or all of the symbols positioned between the reference symbols and the symbols containing the rank information (i.e., the third, fifth, tenth and twelfth symbols of the subframe 113), commencing at the lowest frequency subcarrier edge (sub0) of the subframe 113. Thus, the added ACK/NACK information overwrites or purges the data bits and potentially the CQI information located in the resource elements that are overwritten with the ACK/NACK information. However, forward error correction applied to the data bits and the CQI information enables recovery of the data and, if applicable, the CQI at the eNB.
Thus, as detailed above, the E-UTRA standard requires that a data MCS be provided in a scheduling grant message scheduling transmission of data on a PUSCH and further provides for linkage of the data MCS to the MCS for the respective control information accompanying the data on the PUSCH. However, the standard does not address which MCS should be used for transmission of uplink control information in the absence of data when the transmission of such control information is scheduled (e.g., aperiodically) over the PUSCH by the eNB.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale or to include every component of an element. For example, the dimensions of some of the elements in the figures may be exaggerated alone or relative to other elements, or some and possibly many components of an element may be excluded from the element, to help improve the understanding of the various embodiments of the present invention.